Abstract
Abstract— The kinetics of the oxidation of a homologous series of 4,4′‐di(n‐alkyl)‐bipyridinium (viologen) radicals by Ru(NH3)63+ in vesicle suspensions was studied using laser flash photolysis. The viologen radicals were produced photochemically in the bilayer membrane phase of the vesicles by electron transfer from the triplet state of chlorophyll‐α. At high concentrations of Ru(NH3)63+, the rate of oxidation of the viologen radicals in the aqueous phase was limited by the rate at which the radicals diffused from the membrane to the aqueous phase. The exit rate constant decreased from 2 × 105 s−1 for the methyl viologen radical to 4 × 103 s−1 for the pentyl viologen radical. Both the exit rate constants and the calculated values for the equilibrium association constants of the viologen radicals were unexpectedly insensitive to the length of their alkyl substituents. This, as well as other data, suggests that the radicals that diffused into the aqueous phase tended to remain associated with the membrane‐water interface.
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